Attention has been focused on a foil bearing as a bearing configured to support a shaft of a turbo machine such as a gas turbine or a turbocharger. The foil bearing has bearing surfaces formed of flexible thin films (foils) having low flexural rigidity, and is configured to support a load by allowing the bearing surfaces to be deflected. During rotation of the shaft, fluid films (such as air films) are formed between the shaft and the foils, and the shaft is supported in a non-contact state. In this case, the foils of the foil bearing are flexible, and hence appropriate bearing gaps are automatically formed in accordance with operating conditions such as a rotation speed of the shaft, a load on the shaft, and an ambient temperature. Therefore, the foil bearing is excellent in stability, and hence can be used at higher speed in comparison with general air dynamic pressure bearings.
For example, in Patent Literature 1 below, a foil bearing 100 as illustrated in FIG. 10 is disclosed. The foil bearing 100 includes a foil holder 110 having a cylindrical shape, and a plurality of foils 120 fixed to an inner peripheral surface 111 of the foil holder 110. As illustrated in FIG. 11, each foil 120 includes a top foil portion 121 having a bearing surface, extending portions 122 formed on one circumferential side of the top foil portion 121, and an underfoil portion 123 formed on another circumferential side of the top foil portion 121. Slits 124 are formed at a boundary between the top foil portion 121 and the underfoil portion 123 of each foil 120. The extending portions 122 of each foil 120 are inserted into the slits 124 of another foil 120 (see FIG. 12), and, further, are inserted into each groove 114 formed in the inner peripheral surface 111 of the foil holder 110 (see FIG. 10). The underfoil portion 123 of each foil 120 is arranged between the top foil portion 121 of the another foil 120 and the inner peripheral surface 111 of the foil holder 110, and supports the top foil portion 121 from behind (from a radially outer side).